Preparation of alpha, beta-dichloropropionic acid esters



Patented June 8, 1954 "UNITED STATES "PATENT "OFFICE PREPARATION OF afi-"DICHL'OROPROPIONIC ACID ESTERS William 0. Ney, Jr., SomersetCenter, Mass.,: as-

signer to General Aniline & Film Corporation,

New York, N. Y., a. corporation of Delaware No Drawing. Application October "30,1950, SerialfNo. 193,037

Claims.

.Thisinvention relates to a method :of preparing esters of a,c-dichloropropionic acid from the vcorresponding esters of acrylic acid.

.the. fl-dichloropropionic ester from the resulting reaction mixture was complicated by solvent recovery and was therefore relatively expensive and inconvenient.

It is an object of this invention to provide :an

improved processior producing c-dichloroprm .pionic acid-esters by reaction of the corresponding acrylic acid esters with chlorine, wherein greatly improved yields are obtained, side :reacaction can be carried out in a continuous manner.

According tomy invention, I havfefound that .ozfi-diChlOIOPtOPiOIliC acidesters can be readily prepared, in high yields (e. g. 80 to-90.% .of theory in the case of themethyl ester) by passing the correspondingacrylic acidestenin contact with chlorine gas, .in countercurrent, but preferably concurrent, flow, .through a reaction zonen-in which,- preferably, extensive surface (contact .is maintained between the gaseous and .liquid phases, and wherein the maximum "temperature is maintained at .40 to 200 .C. and preferably :80 to 120 C., the conditions (particularly the pressure) being such as to efiect vaporization of most of the. acrylic acid ester at the maximumtemperature maintained in the reaction zone. The mol ratio of chlorine to theacrylic acid ester passed through said zonecan be varied from 0.75 to 3.2, but 'ispreferably between 0.9 and 1.5. No catalyst is required, and the. presence of materials catalyzing side reactions .or decomposition is preferably avoided. Preferably, a small amount of water is included with the acrylic acid ester, e. g. an amount corresponding to 0.5 to 3% of the ester, to obtain optimum yields. It is also desirable to include a small amount of a polymerization inhibitor such as hydroquinone or ptertiary butyl catechol in the acrylic ester to prevent polymerization thereof.

Under the conditions outlined above, most of the acrylic acid ester is vaporized in the reaction zone, and chlorine :addition'occurs largely as a 'vapor phase reaction. The reaction mixture recovered from the reaction zone, e. g. by cooling, yields a liquid fromwhichzunreacted acrylic estercan. be readily recovered by distillation and recycled .to the reaction zone, while the ,fi-dichloropropionic acid ester can be recovered" in pure form by simple fractionation or steam distillation.

The reaction is conveniently carried out in :a packed column of glass :orother ceramic material containing a packing of similar materials.

The acrylic acid ester'is allowed to fiow downward over the packing on which it is exposed .to chlorine simultaneously passed through the column, preferably in a concurrentdirection. vSince the reaction'is. exothermic, the. desired maximum temperature canordinarily be attained without supplying additional heat. However, in appropriate cases, the column can'be equipped with a jacket cr -similar device for circulating 'a cooling medium in ordernto maintain the temperature within the desired limits, or with a. heating. medium if the desired reaction temperature is not attained 'from the-heat of the reaction.

- Acrylic esters suitable for treatment in accordance with this process are those which can be vaporized withoutdecompositicn at the .temperatures attained in'the reaction zone. These include-especially the acrylic acid-esters of monohydroxyhydrocarbons 0f the saturated aliphatic and cycloaliphatic series, and of the aryl- (saturateda-aliphatic and aromatic series, for exampleg the acrylic esters of methanol, ethanol, .butanol, octanol; dodecanol, octa'clecanol, cyclohexanol, methyl cyclo'hexanol, benzyl alcohol, phenol, and cresol.

The process'of this invention is illustrated in the following examples, wherein-parts arehy weight uriless-otherwise specified.

Example .1

325 grams perhou-r of methyl acr-ylate, stabilized by 0. 25% "hydroquinone and containing 1.5% of watenand-chlorine at the rate" of 337 grams per'hour, were introduced at the top or "a vertical g lasscolumn 2 inches in 'diame'ter "and 2 feet long, packed with glass fiber, having at its base a receiver heated at methyl acrylate reflux temperature to 0.), and an outlet for exhaust gases. The column was operated without a jacket, and the maximum temperature attained therein was to C., the temperature adjacent the inlet and outlet being, respectively, 115 and 79 C. As the mixture passed downward through the column, a liquid product collected in the receiver at the rate of 550 grams per hour, having a specific gravity of 1.275 and a refraction index (N of 1.4486. On fractional distillation of this product, 0.711 mol of methyl a,fi-dichloropropionate (N =1.4506) and 0.175 mol of unreacted methyl acrylate were recovered per mol of methyl acrylate introduced into the column. The yield of methyl a,B-dichioropropionate was thus 86.2% of theory.

Example 2 313 grams per hour of moist methyl acrylate, stabilized with 0.25% hydroquinone, and 696 grams per hour of chlorine were introduced at the top of a glass column 2 inches in diameter and 8 feet long, packed with glass fiber, having a jacket through which cooling water at an initial temperature of 27 C. was circulated at the rate of 25.5 liters per hour. and an exit for exhaust gases were provided as in the preceding example, at the base of the column. The maximum temperature attained in the column during operation was 1055 C., the inlet and outlet temperatures being, respectively 44. and 30 C. The temperature of the eiiiuent cooling Water was C. A liquid prodnot was collected at the base of the column at the rate of 563 grams per hour, having a specific gravity of 1.335 and an index of refraction (N of 1.4550. On fractional distillation, the product yielded 0.782 mol of methyl a,e-dichloropropionate and 0.078 mol of unreacted methyl acrylate per mol of methyl acrylate introduced into the column. This corresponds to a yield of 89.4% of theory.

Increasing the proportion of water to as high as 15% of methyl acrylate has no substantial effect on the yield. Similarly, dilution with inert diluents such as nitrogen, methanol, cyclohexene and benzene has no appreciable effect on the reaction. Countercurrent flow of chlorine lowers the yield, e. g. to about to and results in the formation of larger amounts of high boiling side reaction products. Hence, concurrent flow of chlorine and the acrylic acid ester is preferred.

Instead of methyl acrylate employed in the foregoing example, other acrylic acid esters, such as methyl, ethyl, n-butyl or isobutyl, cyclohexyl, methylcyclohexyl, benzyl, phenyl, acrylates can be similarly converted to the corresponding s-diohloropropionates.

Pressure maintained in the reaction zone can be atmospheric or above orbelow atmospheric pressure, although superatomspheric pressure, exceeding that caused by the back-pressure of the apparatus, is unnecessary. Subatmospheric pressures can be used to insure adequate volatilization of the acrylic ester at the maximum temperature attained in the reaction zone. Ordinarily, however, sufiicient volatilization takes place at atmospheric pressure and without operating under reduced pressures.

As illustrated in the examples, the ester can be conveniently introduced in liquid form, allowing vaporization to occur in the reaction zone. However, the ester can also be introduced into the A. collector vessel and cresyl column in the form of a vapor. While the maximum temperature, as illustrated in the examples, is preferably from 10 to 150 C., higher temperatures up to 200 C. can be used, especially in the case of higher boiling acrylic esters.

Other variations and modifications, which will be obvious to those skilled in the art, can be made in the process as illustrated above, without departing from the scope of the invention.

I claim:

1. A process for the preparation of an ester of ozfi-dlChlOl'ODI'ODiOIIiC acid, which comprises mixing chlorine with the corresponding ester of acrylic acid in the vapor phase, at a temperature from 40 to 200 0., and recovering a,p-dichloro propionic ester from the resulting reaction mixture.

2. A process for the preparation of an ester of a,;3-dichloropropionic acid, which comprises passing chlorine and the corresponding ester of acrylic acid, in a mol ratio of 0.75 to 3.0, through a reaction zone in which the maximum tempera ture is maintained within the range of 40 to 200 C. and the acrylic ester is vaporized, and recovering 0a,}3-dl0h101'013l013i01'1l6 ester from the iixture issuing from said reaction zone.

3. A process for the preparation of an ester of 04,]9-(3110111010D10Dl011i0 acid, which comprises passing chlorine and the corresponding ester of acrylic acid in a mol ratio of 0.9 to 1.50, concurrently through a reaction zone in which the maximum temperature is maintained within the range of 40 to 200 C. and the acrylic ester is vaporized, and recovering a,,$-dichloropropionic ester from the mixture issuing from said reaction zone.

4.. A process for the preparation of methyl u,,8-dichloropropionate, which comprises passing chlorine and methyl acrylate in 2. mol ratio of 0.9 to 1.50 concurrently through a reaction zone in which the maximum temperature is maintained within the range of to C. and the methyl acrylate is vaporized, and recovering methyl a,,8-dichloropropionate from the mixture issuing from the reaction zone.

5. A process for the preparation of an ester of u,e-dicl1loropropionic acid, which comprises flowing the corresponding acrylic acid ester downward through a packed column, introducing a concurrent stream of chlorine gas into said column in a mol ratio relative to the acrylic acid ester of 0.9 to 1.50, maintaining a maximum temperature in the column within the range of 80 to 120 C., and a pressure at which the acrylic acid ester vaporizes at said temperature, and recovering the a,B-dichloropropionic acid ester from the efiluent at the base of the column.

References Cited in the file of this patent UNITED STATES PATENTS Name Date DIanni May 25, 1943 OTHER REFERENCES Number 

1. A PROCESS FOR THE PREPARATION OF AN ESTER OF A,B-DICHLOROPROPIONIC ACID, WHICH COMPRISES MIXING CHLORINE WITH THE CORRESPONDING ESTER OF ACRYLIC ACID IN THE VAPOR PHASE, AT A TEMPERATURE FROM 40 TO 200* C., AND RECOVERING A,B-DICHLOROPHORPIONIC ESTER FROM THE RESULTING REACTION MIXTURE. 